(1) Field of the invention
The present invention generally relates to a developing unit and an image recording apparatus using such, and more particularly to a developing unit and an image recording apparatus using such, in which developing unit a thin developer layer is formed by a thin blade on a surface of a developing roller rotated and in contact with an image carrying medium. The developer is supplied from the thin developer layer to the image carrying medium, so that a developing process is carried out.
(2) Description of related art
A developing unit used in an electrophotographic recording unit, such as a laser beam printer, a copy machine and the like, contains developer such as toner. When the developing unit is operated, a pressure is generated in a housing of the developing unit by operations of an agitator for agitating the toner, a toner supplying mechanism for supplying the toner to a developing roller and the like. In a case where there are various gaps formed on the housing of the developing unit, toner can be spouted by the pressure from the housing via the gaps when the developing unit is operated.
In addition, when the developing unit is replaced, the toner can fall from the housing via the gaps formed in the housing.
In the developing unit, a housing frame 10, a developing roller 11, a thin blade 12, and an elastic sheet 13 are arranged, for example, as shown in FIG. 1. FIG. 1 shows a cross section of an end part of an example of the developing unit. The developing roller 11 is mounted on the housing frame 10 of the developing unit so as to cover an opening (not shown) formed on the housing. The developing roller 11 is rotated in a direction from the thin blade 12 side to the elastic sheet 13 side of the developing unit. The toner in the housing of the developing unit is adhered to the surface of the developing roller 11 via the opening. The thin blade 12 scatters the toner adhered to the surface of the rotated developing roller 11 so that a thin toner layer is formed on the surface of the developing roller 11. The toner is supplied from the thin toner layer formed on the surface of the developing roller 11 to an image carrying medium, such as a photosensitive belt, so that a developing process is carried out.
A gap between the surface of the rotated developing roller 11 and the housing frame 10 is sealed by the thin blade 12 on a upstream side of a developing point at which the toner is supplied from the developing roller 11 to the photosensitive member (the image carrying medium), and sealed by the elastic sheet 13 on a downstream side of the developing area.
Since the developing roller must be rotated, ends of the developing roller 11 cannot be fixed on the housing frame 10. In addition, since the thin blade 12 must be elastically operated, ends of the thin blade 12 can not be fixed on the housing frame 10. Thus, a gap G1 is formed between each end of the developing roller 11 and the housing frame 10 of the developing unit, and a gap G2 is formed between each end of the thin blade 12 and the housing frame 10. These gaps G1 and G2 (indicated by oblique lines in FIG.1) should be sealed to prevent the toner from dispersing through them. As the gaps G1 and G2 form a continuous gap, the two gaps G1 and G2 are conventionally sealed by one sealing member.
However, in a case where the two gaps G1 and G2 are sealed by one sealing member, it is hard for the toner to be completely prevented from dispersing. An optimum sealing member for definitely sealing a gap between a rotated structure and a fixed structure differs from that for definitely sealing a gap between fixed structures. That is, when the sealing member is formed so as to favorably seal the gap G1 between the rotated developing roller 11 and the fixed housing frame 10, it is hard for the same sealing member to definitely seal the gap G2 between the fixed thin blade 12 and the fixed housing frame 10, and vice versa.
Further, a small gap C is formed between the surface of the developing roller 11 and an end part of the thin blade 12 due to the rotation of the developing roller 11, as shown in FIG. 1B. The small gap C extends in a direction approximately parallel to an axis of the developing roller 11. In this case, the toner will leak through the small gap C.
In addition, each end 13a of the elastic sheet 13 is in steady contact with the surface of the housing frame 10, so that the toner is prevented from dispersing through a gap between the end 13a of the elastic sheet 13 and the housing frame 10.
However, it is difficult to form the elastic sheet having a constant length. Thus, in a case where the elastic sheet 13 is formed so that the length thereof is slightly shorter than the constant length, the edge 13a of the elastic sheet 13 can not be in steady contact with the housing frame 10 of the developing unit. In this case, the toner will leak between the edge 13a of the elastic sheet 13 and the housing frame 10. Japanese Patent Laid Open Publication No.62-208073 discloses a sealing member for sealing a gap between the end of the elastic sheet and an end part of the housing frame. However, it is hard for the sealing member to securely seal the gap between the end of the elastic sheet and the housing frame.